1. Anna Serdyuchenko, Victor Gorshelev, Wissam Chehade, Mark Weber, John P. Burrows University of Bremen, Institute for Environmental Physics

2. 2 Atmospheric species detection:  Satellite spectrometers  Available databases for the reference data Challenges of cross-section measurements in laboratory:  Modern demands on the O3 absorption cross- section quality;  Experimental equipment;  Absolute calibration. First results:  Ozone spectra in UV and IR;  Comparison with existing datasets. Introduction and motivation Experimental set-up Analysis of sources of uncertainty Results and Outlook University Bremen, IUP, Molecular Spectroscopy Lab

3. 3 Satellite/airborne/ground spectrometers monitor: Stratosphere: ozone chemistry, volcanic events, solar proton events Troposphere: biomass burning, pollution, arctic haze, forest fires, dust storms, industrial plumes Clouds, aerosols, UV index Introduction and motivation Experimental set-up Analysis of sources of uncertainty Results and Outlook Detected: the solar radiation transmitted, backscattered and reflected from the Earth atmosphere and surface, also direct sun light Absorption spectra cover: O3 O2 NO2 N2O BrO OClO SO2 H2CO2 CO CO2 CH4 H2O GOME, GOME2 (Global Ozone Monitoring Experiment): scanning 4 channels grating spectrometer with nadir-view SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric Chartography): scanning 8 channels grating spectrometer with nadir/limb-view University Bremen, IUP, Molecular Spectroscopy Lab

4. Long-term time-series of O 3 is important for air quality study, Montreal Protocol monitoring of ozone depleting substances, ozone-climate interaction etc Long-term global data sets covering several decades are only available by combining datasets from multiple sensors (satellite spectrometers and ground based instruments: Brewer, Dobson spectrophotometers ). At least two decades of observations with global coverage in several daysSpectrometerSatelliteLaunch GOMEERS-2April 1995 SCIAMACHYENVISATMarch 2002 GOME-2MetOp -AOctober 2006 MetOp - B~ 2012 MetOp - C~ 2016 4 Introduction and motivation Experimental set-up Analysis of sources of uncertainty Results and Outlook University Bremen, IUP, Molecular Spectroscopy Lab

5. 5 Absorption cross-sections can introduce an important error source For GOME, SCIAMACHY, and GOME2 flight models were used to measure absorption cross-section prior to launch. Advantage: exact match of spectral resolution between satellite radiance and cross-sections; Knowledge for instrumental slit function is not needed Introduction and motivation Experimental set-up Analysis of sources of uncertainty Results and OutlookSpectrometerSatelliteLaunch Pre-launch O3 cross-sections GOMEERS-2April 1995GOME FM (Burrows et al. 1999) SCIAMACHYENVISATMarch 2002SCIAMACHY FM (Bogumil et al. 2003) GOME-2MetOp -AOctober 2006GOME2 FM3 (Gür et al., 2005) MetOp - B~ June 2012GOME2 FM21 (Gür et al., 2005) MetOp - C~ 2016- University Bremen, IUP, Molecular Spectroscopy Lab

6. 6 Data setTemperatures, KResolution, nmWavelength, nm GOME FM Burrows et al., 1999 ‏ 202 221 241 273 2930.17 @ 330 nm230 - 800 SCIAMACHY FM Bogumil et al., 2003 203 223 243 273 2930.20 @ 330 nm230 - 1070 GOME2 FM Spietz et al., 2005 203 223 243 273 2930.29 @ 330nm240 – 790 Paur and Bass, 1985203 218 228 243 273 298 <0.025 nm(?) ‏ 245 - 345 Malicet et al. 1995 Brion et al., 1993 Daumont et al., 1992 218 228 243 273 2950.01-0.02 nm 195-345 UV-FTS Voigt et al., 2001 203 223 246 280 293 0.03 @ 230 nm230 - 850 Introduction and motivation Experimental set-up Analysis of sources of uncertainty Results and Outlook http:/ http://www.iup.uni-bremen.de/gruppen/molspec/databases/index.html University Bremen, IUP, Molecular Spectroscopy Lab

7.  SCIAMACHY total O 3 retrieved (with SCIAMACHY reference spectra) are 5% higher than GOME (with GOME reference spectra) in the range 325-335 nm  GOME2 total O 3 retrieved (using GOME2 reference spectra) is 9% higher than calculated with resolution adjusted GOME FM  Spurious instrumental trends in multiple instrumenst time series  Harmonisation of O 3 FM cross-sections from GOME and SCIAMACHY for a consistent retrieval 7 Introduction and motivation Experimental set-up Analysis of sources of uncertainty Results and Outlook University Bremen, IUP, Molecular Spectroscopy Lab

8. The committee "ACSO" ("Absorption Cross Sections of Ozone") was established in spring 2009 by the World Meteorological Organization (WMO) and the International Association of Meteorology and Atmospheric Sciences (IAMAS) to  Review the presently available ozone absorption cross sections  Determine the impact of changing the reference ozone absorption cross sections for all of the commonly used atmospheric ozone monitoring instruments.  Recommend whether a change needs to be made.  The recommendations are to be discussed with the community of the involved experts. The work will be finished within two years after the first meeting in May 2009. 8 Introduction and motivation Experimental set-up Analysis of sources of uncertainty Results and Outlook

9. I.Re-analysis of laboratory data from the measurements campaigns for GOME, GOME2 and SCIAMACHY II.New laboratory measurements should improve absolute scaling and wavelength scaling. should have best possible quality to serve as a most reliable reference source:  wavelength coverage 240–1000 nm;  vacuum wavelength accuracy better than 0.001 nm;  spectral resolution of about 0.02 nm;  absolute intensities accurate to at least 2%;  more temperatures in range 190K-300K. sufficient accuracy to detect a 1% pro decade trend! 9 Introduction and motivation Experimental set-up Analysis of sources of uncertainty Results and Outlook University Bremen, IUP, Molecular Spectroscopy Lab

10. I / I 0 – transmitted intensity with /without absorber,  – absorption cross section OD – optical density, uncertainty depends on precision of measurements A – scaling factor, uncertainty depends on accuracy of the scaling method N – absorber density L – absorption path length 10 Introduction and motivation Experimental set-up Analysis of sources of uncertainty Results and Outlook High precision Low accuracy High accuracy Low precision University Bremen, IUP, Molecular Spectroscopy Lab

11. Echelle spectrometer coverage Echelle spectrometer coverage FT spectrometer coverage 11 Introduction and motivation Experimental set-up Analysis of sources of uncertainty Results and Outlook Note:  varies over 7 orders of magnitude!

12. 12 Introduction and motivation Experimental set-up Analysis of sources of uncertainty Results and Outlook University Bremen, IUP, Molecular Spectroscopy Lab

13. 13 Introduction and motivation Experimental set-up Analysis of sources of uncertainty Results and Outlook

14. 14 Instrument: Echelle Averaged: over 250 scans Time: ~ 5 minutes Source: xenon lamp Introduction and motivation Experimental set-up Analysis of sources of uncertainty Results and Outlook University Bremen, IUP, Molecular Spectroscopy Lab

15. 15 Instrument: Echelle, FTS Averaged: over 2000 (100) scans Time: ~ 30 minutes Source: Xe and deuterium lamps Introduction and motivation Experimental set-up Analysis of sources of uncertainty Results and Outlook

16. 16 I. Reference points, averaged from several datasets II. Least squares fit to the selected dataset III. Absolute measurements of the ozone density: Pressure (ozone is not stable!); Absorption path length; Temperature. Introduction and motivation Experimental set-up Analysis of sources of uncertainty Results and Outlook  – absorption cross section OD – optical density A = N L – scaling factor N – absorber density L – absorption path length University Bremen, IUP, Molecular Spectroscopy Lab

17. 17 Dataset Resolution, nm (FWHM) Wavelength region, nm Current work FTS0.02 – 0.20450 – 1000 Echellet0.02211 – 830 SCIAMACHY0.32 – 1.45230 – 1070 GOME, GOME-20.2 – 0.4231 – 794 High Resolution Brion et al.0.02195 – 830 External datasets: GOME, GOME2, SCIAMACHY, Brion et al (high resolution) First approximation: no resolution matching Introduction and motivation Experimental set-up Analysis of sources of uncertainty Results and Outlook

18. University Bremen, IUP, Molecular Spectroscopy Lab18 Least squares fit for 293K to SCIAMACHY Introduction and motivation Experimental set-up Analysis of sources of uncertainty Results and Outlook

19. 19 Introduction and motivation Experimental set-up Analysis of sources of uncertainty Results and Outlook Least squares fit for 293K to Brion

20. University Bremen, IUP, Molecular Spectroscopy Lab20 Least squares fit for 293K to SCIAMACHY and Brion Introduction and motivation Experimental set-up Analysis of sources of uncertainty Results and Outlook

21. University Bremen, IUP, Molecular Spectroscopy Lab21 Independent measurements in UV at 4 temperatures with Echelle spectrometer Each spectrum is absolutely calibrated from temperature and pressure measurements Introduction and motivation Experimental set-up Analysis of sources of uncertainty Results and Outlook High resolution data by Brion et alCurrent work

22.  Serial measurements of ozone absorption cross-sections:  for temperatures 196 K, 203 K, 223K, 243K, 273K and 293K;.  uncertainty of about 1-2%;  resolution 0.02 nm in the region 240 - 600 nm.  Absolute calibration and validation are in progress  Database release expected by the end of 2010  Other atmospheric species: under consideration 22 Introduction and motivation Experimental set-up Analysis of sources of uncertainty Results and Outlook University Bremen, IUP, Molecular Spectroscopy Lab

23. 23 Thank you for attention !

24. University of Bremen, IUP24

25. University Bremen, IUP, Molecular Spectroscopy Lab25 Least squares fit to Brion et al (293K): Introduction and motivation Experimental set-up Analysis of sources of uncertainty Results and Outlook

26. University of Bremen, IUP, Molecular Spectroscopy Lab26 Introduction and motivation Experimental set-up Analysis of sources of uncertainty Results and Outlook

27. University of Bremen, IUP27 Upgraded cooling system Max possible cooling: down to 193 K Temperature stabilization at intermediate points with step of 10 K Reliable temperature determination (better than 5% accuracy) : Pt sensors, spectroscopic method Upgraded gas pre-cooler features 10 meter Cu pipe bound to fit cryostat bath guaranteed cooling down to cryostat vessel temperature; ozone-friendly internal coating minimal heat gain between precooler ant test cell Sensors: Precooler:  Goals and strategy  Re-analysis  Experimental set-up  Serial measurements and preliminary results

28. University of Bremen, IUP28  Goals and strategy  Re-analysis  Experimental set-up  Serial measurements and preliminary results

29. University of Bremen, IUP, Molecular Spectroscopy Lab29 larger deviations for GOME2 below 325 nm „noise“ in Bass Paur above 335 nm

30. University of Bremen, IUP, Molecular Spectroscopy Lab30 Spietz et al. (GOME2 FM3) – At some temperatures deviation of 2% (223 K, 243K) h

31. University Bremen, IUP, Molecular Spectroscopy Lab31  Relative to NIST database Introduction and motivation Experimental set-up Analysis of sources of uncertainty Results and Outlook

32. University Bremen, IUP, Molecular Spectroscopy Lab32 Cooling: double jacket (vacuum/ethanol) cell, cryostat with pre-cooling: 10 m Cu tube coil with inert coating Control: O2-A band at 760 nm, experimental spectrum: from FTS at 0.5 cm, model spectrum: using HITRAN line parameters accuracy: 5 K or better Introduction and motivation Experimental set-up Analysis of sources of uncertainty Results and Outlook